Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Unrecognized tax benefits that would impact effective tax rate	$ 48
Unrecognized tax benefits, income tax penalties and interest expense	2	$ (4)	$ 3
Unrecognized tax benefits, income tax penalties and interest accrued	21	20
Net current deferred tax assets	400	305
Net noncurrent deferred tax liabilities	174	239
Income taxes paid	950	1,590	$ 1,310
Net operating losses and tax credits	$ 164	$ 138